The physiographic and tectonic setting of Andean high- sulfidation epithermal gold-silver deposits Thomas Bissig, Amelia Rainbow, Allan Montgomery, Alan Clark Thanks to students and collaborators too numerous to mention on a slide. Thanks also to industry partners who funded research on HS systems over the years, most importantly Barrick but also Kinross, IamGold, Eco Oro, Ventana Gold Corp. www.faultrocks.com Bissig Geoscience Consulting
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The physiographic and tectonic setting of Andean high ......structural evolution (protected from erosion somehow). Low-sulfidation deposits in the Andean context are more likely to
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The physiographic and tectonic setting of Andean high-sulfidation epithermal gold-silver deposits
Thomas Bissig, Amelia Rainbow, Allan
Montgomery, Alan Clark
Thanks to students and collaborators too numerous to mention on a slide. Thanks also to industry partners who funded research on HS systems over the years, most importantly Barrick but also Kinross, IamGold, Eco Oro, Ventana Gold Corp.
Examples of well endowed high-sulfidation epithermal deposits
Veladero
Landscape elements from Bissig et al. 2002, Charchaflie et al. 2007
Voluminous volcanism from Oligocene to middle Miocene Reduction of volcanism at ~ 14 Ma
Isolated centers between 13 y 5 Ma. Gradual transition from andesite to dacite and rhyolite Mineralization during this time! Youngest event: Rhyolite of 2 Ma. (post mineral)
Bissig et al. 2001, Winocur et al. 2014 and references therein
Low-T. steam-heated alunite, kaolinite, vuggy quartz, native S
Frontera Deidad Surface ~ 15-17 Ma
Azufreras-Torta Suface 12.5/14 Ma
Los R[ios Surface 6-10 Ma
V a
c a
s H
e l a
d a
s (
1 0
- 1 2
. 7 M
a )
V e
l a d
e r o
A u
- A g
M i n
e r a
l i z a
t i o
n (
6 - 9
. 5 M
a )
I n f i
e r n
i l l o
( 1
4 - 1
6 . 5
M a
)
E s c
a b
r o s
o (
1 7
. 5 -
2 1
M a
)
B o
c a
t o m
a (
~ 3
6 M
a )
Vertical zoning in El Indio belt depending on age and elevation
Steam heated zone
Steam heated zone
Veladero Geology Steam heated zone
Filo Federico pit
Amable pit
Several 100 m of steam heated alteration atop the deposit, implies large vadose zone, dry climate
Holley, 2012
FF
Amable
Erosion and hydrothermal activity, Veladero (Filo Federico) to Pascua
Situation at 9.5 Ma
Situation at 10.5 Ma
Jarosite formation
Veladero
Pascua
Water table drop
Water table drop
Rainbow, 2009
Pierina, Peru
Lagunas Norte: Erosion during mineralization
Montgomery 2012
Montgomery 2012
Yanacocha
Tantahuatay
La Zanja
Sipán
Yanacocha, largest Au mine in world (~2001-2006)
• Mined >30 Million troy oz of a 50 Million tr oz (1500 t) Au resource in low grade (0.5-1 g/t Au) quartz-alunite (high sulfidation) oxidized epithermal deposits
• Value ~$50 B
• Deeper sulfide-bearing porphyry Cu-Au resource with advanced argillic alteration (covellite-enargite-pyrite) contains > 5 M t Cu
• Value ~ $30 B.
Yanacocha complex Au
Kupfertal Cu-Au 4 km
Yanacocha, Peru; 7 Ma of magmatism; 5 Ma of Au(Cu) mineralization Decreased magmatic
volumes, increased SiO2, increased HS Au with
time
~80 % of Au
20
% o
f A
u
Longo et al. 2010 Yanacocha
Yanacocha volcanic stratigraphy
Incr
easi
ng
SiO
2
View from Angostura down the La Baja Trend
Paleosurface
Angostura
La Bodega
La Plata Flat landscape at 3500-3700 m a.sl.
California-Vetas district Colombia
Mod from Rodriguez 2014
Angostura
La Bodega
High elevation paleosurface incised by steep drainages To date no igneous rocks contemporaneous with mineralization known from the district
Reduced lithostatic and hydrostatic load, Facilitates fluid release from magma?
Erosion during hydrothermal activity: favorable for mineralization
Depth of emplacement of porphyry and implications for epithermal deposits
Murakami et al. 2010
Porphyry or epithermal? Gold or Copper or Moly?
Scenario 1: Stratovolcano, shallow intrusion
Au ± Cu porphyry
Barren steam-heated /vuggy qz “telescoped”
Au ± Cu porphyry
Sector collapse/erosion
Depth of porphyry emplacement < 2 km Low density vapor Gold not transported to near-surface
Heinrich et al., 2004
High-sulfidation eptihermal deposits form in two stages: 1. Ground preparation
Shallow exsolution of low density vapor
Heinrich et al., 2004
Py,en
2. Mineralization
Magma exsolves higher density vapor at greater depth.
Scenario 2: Deep intrusion, no volcano
Porphyry Cu-Mo
Epithermal Au (high density vapor)
High-density vapor Capable of transporting Au Vapor must condense into aqueous liquid and physically separate from the porphyry (that’s where the structure comes in).
Scenario 3: Multi stage, porphyry and epithermal (e.g., Yanacocha)
Epith Au
Epith Au
Porphyry Au-Cu
Porphyry Cu-Mo
Several overprinting porphyry intrusive events over several Ma
1
2 3
Example La Pepa, Maricunga belt Au mineralized quartz-alunite ledges are 0.5 Ma younger than porphyry (overprint) At Refugio and Cerro Casale, for example, alunite and porphyry are indistinguishable in age (telescoping), there, quartz-alunite ledges are barren.
Muntean and Einaudi, 2001
Overprint vs. Telescoping
View N across La Pepa
Purpura vein
Conclusions 1
• Deposits are commonly located near age equivalent incising lower elevation landforms (valleys and pediments)
• Geomorphology indicates uplift and erosion concurrent with mineralization.
• Erosion lowers water table at back-scarp and may stimulate boiling and fluid mixing leading to ore formation.
• Mineralization mostly post dates volcanism, in some cases by 100’s of Ma.
Pompeya, La Coipa district Chile
Conclusions 2
Stratovolcanoes? Probably not a good host for high-sulfidation epithermal deposits (but maybe for porphyry Au-Cu).
Look for the porphyry below the high-sulfidation deposit? Yes, there may be one, but it is probably >3 km deep, unless there is indication of several overprinting systems.
Long term preservation of high-sulfidation deposits only possible if favorable structural evolution (protected from erosion somehow). Low-sulfidation deposits in the Andean context are more likely to be preserved over time due to extensional regime and cover by younger sediments.
See also Bissig, Clark, Montgomery and Rainbow 2015, Ore Geology Reviews.
References Bissig, T., Lee, J.K.W., Clark, A.H., Heather, K.B., 2001. The Cenozoic history of volcanism and hydrothermal alteration
in the central Andean flat-slab region: New 40Ar-39Ar constraints from the El Indio-Pascua Au (-Ag, Cu) belt, 29° 20 '-30° 30 ' S. Int Geol Rev 43, 312-340.
Bissig, T., Clark, A.H., Lee, J.K.W., Hodgson, C.J., 2002. Miocene landscape evolution and geomorphologic controls on epithermal processes in the El Indio-Pascua Au-Ag-Cu belt, Chile and Argentina. Econ Geol Bull Soc 97, 971-996.
Charchaflie, D., Tosdal, R.M., Mortensen, J.K., 2007. Geologic framework of the Veladero high-sulfidation epithermal deposit area, Cordillera Frontal, Argentina. Econ Geol Bull Soc 102, 171-192.
Holley, E.A., 2012. The Veladero high-sulfidation epithermal Au-Ag deposit, Argentina: Volcanic stratigraphy, alteration, mineralization, and quartz paragenesis.Unpublished PhD thesis, Colorado School of Mines, Golden, Colorado, 226 p.
Longo, A.A., Dilles, J.H., Grunder, A.L., Duncan, R., 2010. Evolution of calc-alkaline volcanism and associated hydrothermal gold deposits at Yanacocha, Peru. Econ Geol 105, 1191-1241.
Montgomery, A.T., 2012. Metallogenetic controls on Miocene high-sulphidation epithermal gold mineralization, Alto Chicama district, La Libertad, northern Perú. Unpublished PhD thesis, Queen´s University, Kingston, Ontario, Canada, 381 p.
Murakami, H., Seo, J. H., & Heinrich, C. A. 2010. The relation between Cu/Au ratio and formation depth of porphyry-style Cu–Au±Mo deposits. Mineralium Deposita, 45, 11-21.
Rainbow, A. 2009. Genesis and evolution of the Pierina high-sulphidation epithermal Au-Ag Deposit, Ancash, Perú. Unpublished PhD thesis, Queen’s University, Kingston, On, Canada, 277 p.
Winocur, D.A., Litvak, V.D., Ramos, V.A., 2014. Magmatic and tectonic evolution of the Oligocene Valle del Cura basin, Main Andes of Argentina and Chile: evidence for generalized extension. Geological Society of London Special Publication 399, doi:10.1144/SP399.2